The present invention relates to a protocol test device having at least two channels which each have a transmit side as well as a receive side, and more particularly to a method for determining, by approximation, a transmit time of a data package from the protocol test device.
The problem on which the present invention is based is to be explained using the example of an arrangement known from the prior art which is illustrated in FIG. 1. FIG. 1 is a schematic view of the structures of first and second protocol test device channels. Channel 1 and channel 2 are identically structured, each exhibiting a transmit side and a receive side. For testing a test object 10 (shown in dashed lines), a message is first of all generated in a block 12 on the transmit side. In a block 14, this message is then time-stamped and subsequently written into a storage 16, usually of the FIFO type. Depending on the occupancy of FIFO 16, the message to be transmitted is forwarded to the test object 10 at an earlier or later time, with an output signal of the test object 10 being forwarded to the receive side of channel 1. There it first passes a storage 18 on the receive side which is likewise preferably of the FIFO type. Subsequently, the message is time-stamped in block 20 and is finally evaluated in block 22.
Using a switch Stst1, the transmit signal from the transmit side of a particular channel can be guided directly to the receive side of the same channel, thus avoiding the test object 10, in order to check the quality of the transmit signal or the receiving characteristics of this channel of the protocol test device.
Channel 2 is of identical structure, with the respective components being additionally marked “a”. In channel 2, switch Stst2 corresponds to switch Stst1.
Two monitoring switches Smon1, Smon2 allow a switching to pure monitoring operation of a two-channel line between two network subscribers in the position shown in dashed lines. In the position drawn as a solid line, the two network subscribers can be triggered by transmit signals from the protocol test device.
For protocol test devices simulating or emulating communication protocols the transmit time must be determined as precisely as possible. As shown in FIG. 1, the time stamp is assigned before the message to be transmitted is written into FIFO 16. However, the occupancy of FIFO 16 is usually unknown for which reason it cannot be determined precisely when the message is actually transmitted, i.e. when the message actually leaves the transmit side and thus storage 16.
What is desired is to provide a protocol test device of the aforementioned kind which allows a more precise determination of the transmit time of a message, and to provide a method for determining, by approximation, the transmit time of a data package from the protocol test device.